A hearing aid generally refers to an amplification device, which may have a microphone to pick up sounds from the environment surrounding the person wearing the hearing aid or a direct audio input that receives electrical signal from another device, a signal processor to process the sounds, and a receiver to transmit acoustic energy to the user's ear canal or to a coupling device then to the user's ear canal (as in acoustic hearing aids). The receiver may be replaced by a bone vibrator to transmit mechanical energy to the temporal bone (as in bone-conduction hearing aids). The signal processor's processing of the sounds depends on the user's hearing loss and the nature of the sounds.
A cochlear implant generally refers to a device that has a microphone to pick up sounds from the environment or a direct audio input that receives electrical signal from another device, a speech processor to process the sounds and covert them to electric pulses using different speech coding strategies (e.g., CIS, SPEAK, SAS, HiRes), a transmitter to send the pulses across the skull, and a receiver/stimulator to send the pulses to an electrode array implanted in the cochlea to stimulate auditory nerves. FIG. 1 illustrates a block diagram of an exemplary cochlear implant system.
In the past decade, technologies for hearing aids have advanced significantly. For example, many hearing aids have directional microphones and adaptive directionality algorithms to reduce noise interference; some hearing aids have microphone-matching algorithms to maintain the directional performance of the hearing aids; and some hearing aids may also have an automatic-switching mechanism for telecoil-microphone modes, for directional-omni-directional modes, and for different listening programs. These technologies have allowed hearing aid users to have better speech understanding, more listening comfort, and added convenience.
Difficulties in understanding speech in noise have been the most frequent complaints from both hearing aid and cochlear implant users. Research has shown that hearing aid and cochlear implant users have more difficulties in understanding speech in noisy environments than people with normal hearing, depending on the spectral and temporal characteristics of the background noise (Dirks, Morgan & Dubno, 1982; Dorman et al, 1998; Duquesnoy, 1983; Eisenberg, Dirks & Bell, 1995; Festen & Plomp, 1990; Gengel, 1971; Kessler et al., 1997; Plomp, 1994; Skinner et al., 1994; Soede, 2000, Peters, Moore & Baer, 1998, Tillman, Carhart & Olsen, 1970; Zeng & Galvin, 1999). Noise creates difficulties in speech understanding, which may elicit other negative reactions for hearing aid users, such as, annoyance, headaches, fatigue, embarrassment, and social isolation.
From a signal processing point of view, the differences between speech and noise may be explored by their temporal, spectral, and/or spatial characteristics and relationships. Temporally, noise may co-exist with targeted speech at the same instance or they may occur at different instances. Spectrally, the frequency spectrum of speech and noise may overlap or occur at different frequency regions. Spatially, noise may originate from a different spatial angle than the targeted speech, or noise may come from the same direction as the targeted speech.
Multiple technologies have been developed to reduce the detrimental effect of background noise on hearing aids, such as noise reduction/speech enhancement algorithms, directional microphones, microphone matching algorithms, and adaptive directionality algorithms. Speech enhancement algorithms exaggerate the spectral and/or temporal contrast in an attempt to enhance speech intelligibility (Olsen, 2002; Matsui & Lemons, 2001). Noise reduction algorithms are mainly designed to reduce noise interferences. Some noise reduction algorithms take advantage of the spectral separation between speech and noise and some noise reduction algorithms take advantage of the temporal separation between speech and noise. Algorithms that take advantage of the spectral separation between speech and noise detect the frequency bands with speech-like signal dominance or with noise-like signal dominance, and reduce the gain of the frequency bands at which noise occurs (Kuk, Ludvigsen & Paludan-Muller , 2002; Johns, Bray & Nilsson, 2001; Olsen, 2002). Other algorithms attempt to take advantage of the temporal separation between speech and noise. When no speech is detected, the algorithm gradually reduces the gain or increase compression of the hearing aid. When speech is present, the algorithm instantaneously restores the gain to the normal settings (Bachler, Knecht, Launer & Uvacek, 1997; Elberling, 2002). Some of the noise-reduction algorithms are proven to either enhance speech understanding or increase listening comfort for hearing aid users (Bray & Nilson, 2001; Bray & Valente, 2001, Chung, 2002, Chung, 2003).
While noise reduction algorithms take advantage of temporal and spectral separations between speech and noise, directional microphones have reportedly been more effective in reducing background noise originating from different spatial locations than the targeted speech, for both hearing aid and cochlear implant users (Cord et al., 2002; Hawkins & Yacullo, 1984; Killion et al., 1997; Ricketts et al., 2001; Wouters & Vanden Berghe, 2001, Wouters et al., 2002). Many hearing aid manufacturers have also implemented various advanced algorithms to make directional microphones more effective. These advanced algorithms include adaptive directionality algorithms to detect the location of noise and change the polar pattern of the directional microphone system so that noise is maximally reduced. This feature may be especially useful if the relative location of speech and noise changes in space (Ricketts & Henry, 2002). Other such advanced algorithms include in-situ microphone matching algorithms to match the frequency response of the microphones when the hearing aid is worn in the ear in order to compensate for microphone drift and to obtain maximum directional performance. Although some cochlear implant systems may offer directional microphone technology, few cochlear implant manufacturers have implemented these advanced algorithms in their products.
In addition, many hearing aid manufacturers have developed automatic switches for switching between directional and omni-directional modes, among different listening programs and switchless telecoils. Directional microphones are generally used in noisy environments to reduce noise interference, while omni-directional microphones are generally preferable in quiet environments or when there is wind noise. Usually, the switch between the two modes is accomplished manually. Automatic switch algorithms for different microphone modes can automatically turn the hearing aids to directional mode in noisy environments and to omni-directional mode in quiet environments. For example, when a hearing aid user walks from a quite room to a noisy party, the hearing aids would automatically switch from omni-directional mode to directional mode. When the person walks away from the crowd, the hearing aid would automatically switch back to omni-directional mode. Similarly, the automatic switch algorithms for different listening program can detect the characteristics of incoming sounds, make inferences of the environment that the user is in, and automatically switch to appropriate listening program for the user. In addition, switchless telecoils can automatically switch to telecoil mode when a magnetic field is detected (i.e., when a telephone headset is positioned near the ear), and automatically switch back to microphone mode when the magnetic field disappears (i.e., when the telephone headset is moved away from the ear). Automatic switches can reduce time delays associated with manually switching between the different modes. Automatic switches also offer considerable convenience for hearing aid users, especially for older users whose fingers may not be as sensitive as younger users. These advanced options are not available for cochlear implant users.
FIG. 1 illustrates a block diagram of an exemplary cochlear implant system.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of ordinary skill in the art through comparison of such systems with the present invention.